This invention relates to the field of heat exchangers in which heat from an existing source is utilized to heat water or other fluid which is then utilized for some other heating purposes.
One of the problems with prior art devices of this kind is the heat loss at the heat generating source which results from cold water or other cold fluid being piped into the vicinity of the heat source which reduces the heat needed for its primary purpose or function. For example, heat exchanger coils in a kitchen range used for cooking or baking will draw heat away from the primary cooking and baking function of the range if a portion of the heat is constantly needed to raise the temperature of the fluid flowing in the heat exchanger coils. In accordance with the present invention this problem in large part is overcome by providing an intermediate holding tank in which the water temperature has not been raised to its final end use level so less heat is taken up by the heat exchanger coils to reach that intermediate temperature. Also the unheated water from the public water supply is first fed into the intermediate holding tank which contains already heated water in the upper portion. The temperature of the incoming water from the public water supply is therefore raised somewhat before being fed through the heat exchanger coils, all of which tends to reduce the heat loss taken away from the primary purpose for which the heat source is originally provided. The temperature of the water after flowing through the heat exchanger coils in accordance with this invention is not raised to the high level needed for a particular purpose, such as hot water for washing dishes, bathing and the like, as it normally flows from a hot water faucet, but the temperature of the water is raised to an intermediate level and then fed to a normal hot water heater which completes the heating process raising the temperature to whatever level desired. The same principle can be applied to heated water furnished for other purposes such as adding to a hot water heating system for a building and the like.
Examples of prior art devices which have some of the disadvantages and problems solved by the present invention include U.S. Pat. No. 4,250,864 disclosing a heat exchanger which also functions as a grate for a stove. The grate comprises an arrangement of tubing through which a fluid is directed which enters the heat exchanger directly from an outside source rather than from an intermediate holding tank. U.S. Pat. No. 4,048,962 discloses a heat exchanger comprising a water tank in which three pipes or tubes extend through the water tank carrying smoke from a furnace as it passes from the furnace to a chimney for eventual discharge. U.S. Pat. No. 4,046,189 discloses a hot water heater which heats the water by circulating steam or high temperature water from another source through the tank thereby heating cold water which is drawn in from an external source. The purpose of the invention disclosed in that patent is to provide relatively instantaneous hot water without requiring a large holding tank.
U.S. Pat. No. 3,672,444 discloses a water heating system in which cold water is supplied to a holding tank with a shroud extending into the holding tank having tubing within the shroud connecting to an external source of heat such as steam or hot water. The cold water in the holding tank comes in contact with the heated tubing and is heated in that manner for eventual discharge as hot water. U.S. Pat. No. 2,743,718 discloses a kitchen range in which heating coils are provided to take up heat from the range for the purpose of heating water stored in the reservoir in the range cabinet itself. U.S. Pat. No. 2,095,052 discloses a stove for cooking which has pipes extending into the heating area for the purpose of heating water which is then directed elsewhere for use. U.S. Pat. No. 914,085 discloses a heating range in which cold water is drawn from a city supply source into a chamber connected to the range. The cold water is heated from heat generated by the range after which it is directed to a hot water system for the house. None of the foregoing examples of heat exchangers known to the prior art include the feature of an intermediate holding tank in which cold water from an external source is flowed into an intermediate holding tank having partially heated water already stored therein before being fed to the heat exchanger coils. Neither do such prior art devices disclose the idea of returning heated water from the heat exchanger coils to an intermediate holding tank for subsequent delivery to a main hot water heating device of some kind. Less heat is thereby diverted from the heat exchanger coils in accordance with this invention since its purpose is as a booster to partially raise the temperature of the water rather than attempt to raise it completely to the level needed for a particular end use by means of the heat exchanger coils alone.